Hi,
some words about the 78 series regulators amd capacitors.
Regulators are pretty failsafe. I just don't remember if they have overheat protection (check the datasheets). I once serviced a Yamaha ME-30 (the Stevie Wonder - "I just called" has the same sound, I found out :). The problem was a shorted electrolyte capacitor after the 78xx (05 /09 / 12, can't remember). I recall replacing the regulator at first because there was no voltage at the output. But the regulator wasn't damaged. As soon as I spotted and replaced the faulty cap, everything worked fine. So, the 78xx handled output shorting. Also, I learned that a dead capacitor may not break anything else.
After fixing a number of devices by replacing capacitors only, I recommend you always begin with them if it's likely a power issue. Electrolytes, no other types. Medium sized, not the smallest or biggest (depending on the device, there may not be large capacitors). By the numbers: usually 470 to 2200 micro F and from 15 to 63 volts.
Sami Jumppanen
http://netti.nic.fi/~some-e
- SGS2 -
I did a 7805 replacement once, but I didn’t take any pictures and I sold that one a few years ago. I removed EVERYTHING in the +5V regulator circuit, Q1, Q2, Q3, Q15, Q16, D3, D4, D24, C1, C2, C3, R2, R3, R4, R5, R6, R7, R12, R13, VR1. I believe I soldered the 7805 in the holes for Q3, but only one of the three pins was connected where it needed to go, so I cut the traces from the other two pins and soldered a couple wires to where they needed to go. It worked great, but the 7805 got a little warm. It didn\u2019t ever seem to get hot enough that it would need a heat sink though. Wish I had some pictures. It may seem like a lot of work, but I think it was still easier than trying to debug that old regulator circuit. There is no point in touching Q18 on the \u20135V side until you are sure the +5V is solid.Don BackshallFrom: josh.nursing@gmail.comSent: Sunday, March 9, 2014 1:10 PMSubject: [korgpolyex] Power circuit repair.I am looking to solve the power issue completely once and for all in the Poly-800. What are the parts that I can order for repair and replacing existing ones?
I listed Q1, Q3, Q16, Q18 and a 7805 for now. Anything else I should pay attention to? Any modern parts are welcome.